In the past, wellbores were drilled more or less straight down into the earth in order to penetrate target zones selected by the geologist. If the target zone was to be drilled through at a different point, then the rig was moved to a different position on the surface above that point and the well redrilled into the target. As might be expected this was expensive, so drillers learned to cause a well to deviate from the vertical at a point far enough above the target to angle over to the new target point. This process was called sidetracking the well. With experience, and improvement in the tools needed to perform this task, new applications for directional drilling were considered. Horizontal drilling techniques are a result of the application of advanced directional drilling to solve geological and reservoir engineering problems associated with the production of oil and gas from certain reservoirs.
The first horizontal wellbores were drilled vertically down to a point above the target formation then the directional driller directed the wellbore sideways in a curve until the wellbore was being drilled nearly horizontal in the target formation. Since the target zone was not always a flat evenly dipping formation, there arose a need to provide the directional driller with information about the target orientation in order for him to maintain the drill path in the target. This caused the development of tools and techniques to provide this information.
The first method used to steer a horizontal well was for the geologist to give the directional driller an estimate of the dip rate of the target formation along the expected drill path and analyze the cuttings coming out of the borehole to see if the drill path was staying within the formation. This method of steering worked only for thick targets with little or no changes in dip rate. But as the need for better steering developed, new tools were developed that provided the geologists with petrophysical measurements of the formation while drilling the well called MWD (Measurements While Drilling). This information allowed the geologist to see on a log of formation petrophysical information, if the borehole had been drilled within or outside the target formation. This form of steering provided good information about the drilled wellbore with respect to the target, but changes in the dip of the target and/or faulting could only be known after the drill path had exited the target, requiring the directional driller to try to steer back into the target. This restriction made horizontal drilling ineffective in certain complex geological situations.
Past targeting techniques provided only information about where the path of the well had already gone using well log correlations. When the well path encountered a change in the dip rate of the target interval it required the operator to traverse through the stratigraphic section in order to provide the operator with a correlative log section to determine the new dip of the target section, then requiring a major course correction to get back into the target followed by another correction after reacquiring the target to establish the new dip rate. Depending on the frequency and severity of the dip changes in the path of the well this process can severely decrease the effectiveness of steering operations at extended reaches and reduce the amount of time that the hole is in the target zone, thus possibly affecting the performance of the well.
Thus, there has been a need in the art to provide a better method for adjusting the drill path prior to drilling and while drilling is progressing towards the target or along the target path. Thus, the art has needed a method of steering that allows the geologist the ability to provide the directional driller information about the direction to steer by anticipating where the target is in advance of the borehole in a three dimensional picture. The present invention provides such a map and for revised mapping as the drilling progresses. This three dimensional roadmap of the target zone is the tool needed to steer the wellbore to any point within the target even in very complex targets with many abrupt dip changes and/or faulting, that would be impossible to steer through with the prior art. The target may be a specific point or may be a number of specific points. Thus, the target may be a target point or a target line (path). The present invention has many advantages which include providing an initial map of the target path to allow planning of the drilling operations, providing a corrected target path based in part on actual data determined as the bore progresses, allowing for early correction of the drill bit direction saving time and expense.
The process of the present invention also has the following advantages:
A. Provides the ability to anticipate changes in the dip rate of the target zone. PA1 B. Reduces the frequency and duration of targeting slides. PA1 C. Eliminates the need to traverse section in order to establish a new correlation and dips after a dip change. PA1 D. Provides a true three dimensional targeting technique that provides information about dip changes as a result of changes in drill azimuth. PA1 E. Reduces the number and severity of doglegs allowing for better steering and reducing the torque in the hole. PA1 F. Reduces the well cost as a result of reducing slide time in the well. PA1 G. Improves the well performance.
1. Extends the reach of the well. PA2 2. Makes course correction slides quicker and more effective even in extended reach wells and multi-dimensional wells.
Other advantages of the present invention will become apparent from the detailed description.